"O God, Creator and Redeemer of human nature, who willed that your Word should take flesh in an ever-virgin womb, look with favor on our prayers, that your Only Begotten Son, having taken to himself our humanity, may be pleased to grant us a share in his divinity."
Another way the Church prays during these seven days is with what are called the "O Antiphons". Called this simply because in the Latin they all begin with O but prayed in the Church at the end of Advent for more than one thousand years. Each Antiphon invokes the coming of the Messiah, beginning with a biblical title and closing with a specific petition. These antiphons are sung at evening prayer and also have been added to the liturgy for the Gospel acclamation (the Alleluia) during Mass. The traditional hymn we know so well, O Come, O Come Emmanuel is based on these antiphons as well. For example: here is today's "O Antiphon": O Wisdom, O holy Word of God, you govern all creation with your strong yet tender care: Come and show your people the way to salvation. This website shows the antiphons for each day and a beautiful description of each.
This prayerful video also describes the antiphons: